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Sunday, November 25, 2007

An Explosion of Juliasby Ro Wauer

I’ve never approved of describing a sudden population increase of any animals, whether mammals, herps or bugs, as an “explosion.” It doesn’t seem appropriate. But now, with the unbelievable numbers of Julias (Heliconian iulia) that have suddenly “invaded” our Mission Valley, Texas yard, the term explosion seems most appropriate. During the second and third weeks of November, Betty and I have counted more that 200 individual Julias at one time in our yard. High estimates have reached 300. They were attracted to the numerous blooming crucitas and white bonesets (Eupatorium odoratum & E. wrightii), apparently finding these two shrub species to their liking. Fresh individual Julias seemed to appear daily, perhaps replacing those that died or wandered away.

Although the peak boneset blooms lasted only about two weeks, most of the two dozen or so crucita shrubs remained in flower for an additional five to six weeks. As the bonesets faded, the crucitas received even greater attention from Julias. And when some of the crucitas began to fade, the constantly flowering sky-flowers (Duranta erecta) and lantanas (Lantana sp.) attracted their attention.

This year (2007) is not the first time we have recorded Julias in our yard, although never before have the numbers been so great. Since keeping almost daily (except when away from home) records of our butterfly observations, starting in 1996, our first Julia sighting was on May 21, 1999. Since then Julia sightings have been sporadic and widely scattered. Our records included only one or two individuals during May, June and July, a slight increase in August, more numbers after mid-September through most of November, and none after December 12. But daily numbers never exceeded seven individuals. Until this year!

What has triggered this 2007 explosion of Julias? It must relate to the record rainfall in Victoria County. Our yard does not contain an abundance of passion vines (Passiflora sp.), Julia’s larval foodplants, although the adjacent private (nonaccessible) woodland (approx. 2 X 4 mile) undoubtedly does possess scattered Passiflora species; P. foetida, P. incarnata, P. lutea, and P. tenuiloba are all possible. The majority of Julias, because of their abundance, assumedly emerged from nearby sites. Probably our fall population also included strays from the south.

Although Julias were our lepidopteran centerpiece this fall, much greater than normal numbers of Zebra Heliconians (Heliconius charithonia) and Sickle-winged Skippers (Eantis tamenund) also were present throughout the same period. Other species recorded in larger than normal numbers included Long-tailed Skippers and Dorantes Longtail (Urbanus proteus & U. dorantes) and Ocola Skippers (Panoquina ocola). But at least three species that usually occur in good numbers during October and November, were seldom seen or did not put in an appearance at all: Lyside Sulphur (Kricogonia lyside), American Snout (Libytheana carinenta), White Peacock (Anartia jatrophae), and Common Mestra (Mestra amymone).

The amazing number of Julias provided some unusual observations. Early morning walks around the yard, before Julias became active, revealed many individuals perched alone where they apparently had been the previous evening, on various shrubs and even on the ground. The closely-related Heliconians typically gather at colonial roosts each night. We found Julias to be some of the earliest active butterflies, along with Zebras and Monarchs (Danaus plexippus). We also found that Julias seek moisture more than most species. We often found several individuals scattered on the lawn or ground after each watering, not puddling in groups, but individuals scattered about. And by mid-November, mating pairs increased significantly.

Also by mid-November, many of the “old-timers” showed their age by their fading colors. Instead of showing deep orange, their changing wings revealed a variety of patterns. Some of these were fascinating and truly unusual. Especially females, with their more mottled undersides, changed from orange to yellow. Our yard of Julias has offered a new and unexpected mosiac of patterns and colors. But then, like other indicators of the end of summer, our circus of Julias rapidly declined.